The invention relates to devices for communicating between telematic equipments on the one hand and other telematic equipments or centralized services on the other hand.
In the specification, the term "telematic equipment" refers to equipments providing for electronic mail between terminals (telex, fax, teletex, file transfer), electronic post, data bank access and information center access. Moreover, the term "component" refers to one or several electronic circuits included in a single package.
Administrations of different countries are beginning to set a new type of network for progressively taking the place of the current switched network. This network is a digital one called "integrated services digital network". Such a network is provided for allowing a more reasonable, more efficient and cheaper implementation of current applications, with a better transmission quality.
Because telematic equipments provided for current switched network are yet in use and integrated services digital network is progressively established, a requirement is that current users may use services of this network without buying completely new equipments. So, it is required that some devices allow use of current telematic equipments with this new network.
Some devices called "adapters" are currently available. These adapters are for providing, at the side of telematic equipment, conditions simulating conditions of analogue switched network which have not been the subject of a complete international standardization. These adapters always include for this reason, at the side of the network, a specific circuit and, at the side of a telematic equipment, subscriber handling circuits which are not very integrated and so are relatively bulky and costly.
When a telematic equipment communicates through a switched network, it is connected to this network by a modem (modulator-demodulator). Such a modem always includes two groups of circuits, a first group (often including only one component) providing for the proper modem function, and a second group comprising subscriber line handling circuits, this group including several relatively bulky and costly components.
Subscriber line handling circuits of adapters and modems have a power consumption so high that they have to be connected to a specially provided power source (either specific or common with related telematic equipment).
The paper Electrical Communication, vol. 61, n.degree. 1, 1987, pages 72-80, Harlow, Essex, GB, by D. Adolphs et al: "Subsets, terminals, and terminal adapters for the public ISDN", the paper Wescon Conference Record, vol. 31, 1987, communication 20/75, pages 1-7, Los Angeles, Calif., U.S., by C. Stacey: "Build your own ISDN terminal/terminal adapter", the european patent application n.degree. 238 255, the paper Electronique Industrielle, n.degree. 8, December 1986, pages 32-40, Paris, FR, by H. Geyer: "Le reseau numerique a interation de services", the paper IEEE International Conference on Communications'86, Toronto, 22-25th June 1986, vol. 3, pages 47.3.1-47.3.5, p. 1504-1508, IEEE, New York, U.S., by J. Chatterley et al.: "The ISDN PC: a flexible voice date workstation", and the paper Commutation & Transmission, vol. 9, n.degree. 3, 28th September 1987, pages 35-50, Paris, by J.-L. Lavoisard et al.: "Les installations terminales d'abonnes" all indicate the possibility of designing a board for a computer forming an adapter connected between a telematic equipment and a digital network. The documents, when they are not too concise, indicate a distinct power source and subscriber line handling circuits.